Exception while empty cache doesn't adhere to ordinary stale behavior

[jonasswiatek]

A cache item with state Exception can never enter a stale-state. This means that a failing service during an empty cache scenario will never be able to enter a proper stale mode (i.e. sleipner will block all threads while waiting for the delegate to return) every 10 seconds under these conditions.

Some rewriting needs to be done to avoid this.
@Gissues:{"order":50,"status":"backlog"}